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Path: utzoo!mnetor!seismo!lll-lcc!ptsfa!ihnp4!inuxc!pur-ee!uiucdcs!uiucdcsp!nicholl
From: nicholl@uiucdcsp.cs.uiuc.edu
Newsgroups: comp.lang.smalltalk
Subject: fun with blocks
Message-ID: <80500003@uiucdcsp>
Date: Wed, 8-Apr-87 17:30:00 EST
Article-I.D.: uiucdcsp.80500003
Posted: Wed Apr  8 17:30:00 1987
Date-Received: Mon, 13-Apr-87 04:24:35 EST
Lines: 49
Nf-ID: #N:uiucdcsp:80500003:000:1219
Nf-From: uiucdcsp.cs.uiuc.edu!nicholl    Apr  8 16:30:00 1987



------------------------------

Blocks that "call" themselves can do "recursion". Here is
an example that computes factorial:


-------------------------------------------------------------------
'From Smalltalk-80 version T2.2.0, of March 13, 1986 on 7 April 1987 at 2:26:53 pm'!



!Integer methodsFor: 'factorization and divisibility'!

fac
	| loop |
	loop _ [:num :acc | num == 0
				ifTrue: [^acc]
				ifFalse: [loop value: num - 1 value: acc * num]].
	loop value: self value: 1! !

-------------------------------------------------------------------

This can be used to implement a message-passing version of whileTrue:.
Informal tests show that it runs at about 25% of the speed of the 
standard version produced by the Compiler.


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'From Smalltalk-80 version T2.2.0, of March 13, 1986 on 6 April 1987 at 9:16:33 pm'!



!BlockContext methodsFor: 'controlling'!

whileTrue2: aBlock 
	| loop |
	loop _ [:expr | expr
				ifTrue: 
					[aBlock value.
					loop value: self value]
				ifFalse: [^nil]].
	loop value: self value! !

-------------------------------------------------------------------


                            --Sheldon Nicholl